Serotonin was discovered in the late 1940s and is present in both the peripheral and central nervous systems [Physiol. Res, 60 (2011) 15-25; Psychopharmacology 213 (2011) 167-169]. Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter of the indolalkylamine group that acts at synapses of nerve cells. Seven distinct families of serotonin receptors have been identified and at least 20 subpopulations have been cloned on the basis of sequence similarity, signal transduction coupling and pharmacological characteristics. The seven families of 5-HT receptor are named 5-HT1, 5-HT2, 5-HT3, 5-HT4, 5-HT5, 5-HT6, and 5-HT7 and each of these receptors in turn has subfamilies or subpopulations. The signal transduction mechanism for all seven families have been studied and it is known that activation of 5-HT1 and 5-HT5 receptors causes a decrease in intracellular cAMP whereas activation of 5-HT2, 5-HT3, 5-HT4, 5-HT6, and 5-HT7 results in an increase in intracellular IP3 and DAG. The 5-HT pathways in the brain are involved in CNS disorders. The neurotransmitter binds to its a G-protein coupled receptor and is involved in a wide variety of actions including cognition, mood, anxiety, attention, appetite, cardiovascular function, vasoconstriction, and sleep among others [ACS Medicinal Chemistry Letters 2 (2011) 929-932; Physiol. Res, 60 (2011) 15-25].